The present invention relates to ground propulsion assemblies for aircraft and more specifically to mechanisms for coupling and decoupling ground propulsion assemblies from aircraft wheels.
Typically, an aircraft is propelled and maneuvered on the ground during taxi either indirectly by a wheel tug pulling on a towbar connected to the front landing gear of the aircraft, or directly using the engines of the aircraft to propel the aircraft on the ground. Using a wheel tug and towbar to move and position the aircraft on the ground is inefficient because the aircraft is dependent on ground support personnel and equipment and often must wait until ground support is available. Using the engines on the aircraft to propel the aircraft on the ground is also undesirable as it is an inefficient use of relatively expensive jet engine fuel and poses a safety risk to ground personnel who must remain clear of engine exhaust flows. Furthermore, the aircraft cannot use its own engines to push itself backwards out of the gate as the blast created by the reverse thrust of the engines could damage terminal structures and/or kick up dust and debris that could be ingested by the engines and potentially damage the engines. Thus, an aircraft that uses its own engines to propel itself on the ground may still have to rely on a wheel tug, towbar, and ground personnel to move the aircraft out of the gate and to a safe distance away from the terminal.
Another alternative that has been used to propel an aircraft on the ground is to use an electric motor mechanically coupled to the wheels of the aircraft to power the wheels. During take-off and landing, the electric motor is mechanically decoupled from the wheels so that the wheels can spin freely without resistance from the electric motor and its accompanying mechanical components. Once the aircraft is on the ground and has decelerated on the runway, a clutch assembly is used to mechanically couple the electric motor with the wheels and propel the aircraft at low speeds on the ground. However, the clutch assembly typically employs a relatively complicated and expensive assembly of electro-mechanical actuators, linkages, and gears to mechanically couple and decouple the electric motor from the wheels. Furthermore, the clutch assembly is not sufficiently reliable as it is sensitive shock. The aircraft also would typically utilize expensive power electronics to control the speed and direction of the electronic motor.